The present invention relates to a semiconductor device fabricating method; and, more particularly, to a method for forming a fine pattern in a semiconductor device through the use of an ArF exposure source.
In recent times, a photolithography process has been widely used as a technology for forming a fine pattern required for achieving high-integration semiconductor devices. Therefore, it is very important for the high-integration of the semiconductor devices to improve the resolution of the photolithography.
In general, the photolithography process is performed through two processes, i.e., a process of forming a photoresist pattern and a process of etching a non-pattern area of an etch-target layer by using the photoresist pattern as a mask to thereby obtain a desired pattern, e.g., a contact hole, a bit line, etc. Herein, the photoresist pattern is made by coating a photoresist film on the etch-target layer, exposing the coated photoresist film by using a prepared exposure mask and developing an exposed or unexposed portion of the coated photoresist film by using a chemical solution.
Meanwhile, a critical dimension (CD) of the desired pattern formable through the photolithography process is determined by a wavelength of a light source used in the above exposure process because the CD of the desired pattern is decided depending on a width of the photoresist pattern formable by the above exposure process.
After mass production of semiconductor products including dynamic random access memories (DRAMs) started, the photolithography has made rapid progress. The integration of the DRAM has increased about 4 times every 3 years and the integration speed of other memory devices is about 2 or 3 years later than that of the DRAM. As a result, a product design has developed from 0.8 xcexcm of 4M bit DRAM to 0.13 xcexcm of 4G bit DRAM. Now, non-optical photolithography is emerging.
The resolution of the optical photolithography is inversely proportional to a wavelength of an exposure source. Therefore, an early stepper adopting an exposure scheme of xe2x80x9cstep and repetitionxe2x80x9d used a light source providing a wavelength of 436 nm (g-line) and a wavelength of 365 nm (i-line) and, now, it is using a scanner type exposure equipment or a stepper utilizing deep ultra-violet (DUV) having a 248 nm wavelength (KrF excimer laser).
In the optical photolithography, there have been many developments in materials such as chemically amplified resist (CAR), in a processing aspect, such as tri-layer resist (TLR), bi-layer resist (BLR), top surface imaging (TSI), anti-reflective coating (ARC), etc., and in a mask aspect, such as a phase shift mask (PSM), optical proximity correction (OPC), etc. as well as in the exposure equipment itself, such as a lens having a numeral aperture higher than 0.6 nm and hardware.
The 248 nm DUV photolithography was usually utilized in forming products having a design rule of 0.18 xcexcm since it had many defects such as a time-delay effect, material dependency and so on. Therefore, in order to fabricate products having a design rule lower than 0.15 xcexcm, there needed new DUV photolithography employing a wavelength of 193 nm (ArF excimer laser). However, since it was impossible for this DUV photolithography to form a pattern lower than 0.1 xcexcm although various technologies are employed to enhance the resolution, photolithography using a new light source has developed.
As a result, there have been introduced exposure equipments using an electronic beam and an X-ray as the light source. In addition, an extreme ultraviolet technology using a weak X-ray as the light source is developing.
The early exposure equipment employed an exposing scheme where a mask was located on an upper portion of a substrate to be close to the substrate and its focus was adjusted with operator""s eyes. Then, as this technology was developing, the resolution was enhanced by reducing a gap between the mask and the substrate and the exposure was achieved through soft contact or hard contact (lower than 10 xcexcm) according to the gap size.
Recently, as there have developed an exposure equipment using KrF laser having a wavelength of 248 nm as the light source, photoresist materials and other incidental technologies, it becomes possible to form a pattern having a design rule lower than 0.15 xcexcm.
Now, there is developing a technology capable of forming a fine pattern ranging from 0.11 xcexcm to 0.07 xcexcm by using an exposure equipment employing ArF laser having a wavelength of 193 nm. The DUV photolithography has high resolution and good DOF (depth of focus) property compared to the i-line, whereas it is not easy to control its manufacturing process. This process control problem is resulted from an optical cause due to a short wavelength and a chemical cause induced by using chemically amplified photoresist. As the wavelength is shorter, a CD tilting phenomenon due to a static wave effect and an engraving phenomenon of a reflective light due to a material phase become severe. The CD tilting phenomenon represents a phenomenon where a line thickness is periodically changed since a degree of interference between an incident light and a reflected light varies according to a thickness difference of a substrate film or that of a photoresist film.
Since the DUV process uses the chemically amplified photoresist to improve the optical sensitivity, there occur problems such as post exposure delay (PED) stability and material dependency, which are related to the chemical reaction mechanism. Therefore, one core subject of the ArF exposure technology is to develop new photoresist materials for the ArF exposure, i.e., new ArF photoresist materials. However, since a benzene ring cannot be contained, it is not easy to develop the photoresist material for the ArF exposure. The benzene ring has been contained in the photoresist for the i-line and KrF exposure so as to secure durability in a dry etching process. However, if the benzene ring is contained in the ArF photoresist materials, the absorbency at the 193 nm wavelength of the ArF laser becomes high and, therefore, the transparency is deteriorated. As a result, there occurs a problem of making a lower portion of the photoresist unexposed.
Therefore, there are in progress researches for developing photoresist materials capable of securing the durability in the dry etching process without containing the benzene ring, having a strong adhesive force and being developable at 2.38% TMAH. So far, many companies and institutes are publishing a lot of research results.
Currently, commercially available ArF photoresist materials include COMA (CycloOlefin-Maleic Anhydride), a polymer type belonging to an acrylate family, or their combination, which contains the benzene ring therein.
Referring to FIG. 1, there is exemplarily shown a cross-sectional view of pattern deformation and contact defects in a self-aligned contact (SAC) etching process for forming a landing plug contact (LPC) hole by using the ArF photoresist.
As illustrated in FIG. 1, there are sequentially formed a plurality of gate electrodes 11 and hard masks 12 on a substrate 10. Then, an insulating layer 13 for spacers is coated along the processing profile. An interlayer dielectric layer 14 is deposited on the insulting layer 13 and etched through an SAC etching process to thereby open a region between gate electrodes 11.
In the SAC etching process, fluorine-based gas was used as etching gas to obtain a desired etching profile. As a result, there occurs deformation in the photoresist pattern such as xe2x80x98Axe2x80x99 in FIG. 1, which is due to weak durability of the ArF photoresist pattern.
Furthermore, if there occurs misalignment in an over-etching process for avoiding the defect in the contact hole forming process, parts of the gate electrode 11 and the hard mask 12 are lost as shown in xe2x80x98Bxe2x80x99 of FIG. 1, resulting in the deterioration of electrical properties of devices. Although there does not occur the misalignment, a width of the contact hole becomes narrower as depicted in xe2x80x98Cxe2x80x99 of FIG. 1, leading increased contact resistance.
Moreover, although there is not illustrated in drawings, when forming contact holes such as an LPC hole through the photolithography using the ArF exposure source, there may occur striation in an ArF photoresist pattern, clustering of photoresist or plastic deformation, and wiggling of the photoresist during the contact hole being etched.
Accordingly, there is required to enhance the weak durability and weak physical properties of the ArF photoresist materials for the fluorine-based gas.
It is, therefore, an object of the present invention to provide a method capable of forming a narrow fine pattern in a semiconductor device by minimizing deformation of an ArF photoresist pattern by properly adjusting an etching temperature.
In accordance with an aspect of the present invention, there is provided a method for forming a fine pattern of a semiconductor device, comprising the steps of: (a) providing a semiconductor substrate; (b) sequentially forming an etch-target layer to be formed as the fine pattern, an anti-reflective layer and a photoresist film on the semiconductor substrate, performing photolithography for the photoresist film by using an ArF exposure source to thereby form a photoresist pattern; (c) etching the anti-reflective layer and a portion of a non-pattern area of the etch-target layer at a first substrate temperature with fluorine-based gas and argon gas by using the photoresist pattern as an etching mask; (d) etching a remaining portion of the non-pattern area of the etch-target layer at a second substrate temperature higher than the first substrate temperature with fluorine-based gas and argon gas to thereby form the fine pattern; and (e) removing the anti-reflective layer and the photoresist pattern to thereby form the fine pattern.